1. Epic GamesDeveloper
  3. FForkProcessHelper

FForkProcessHelper

Helper functions for processes that fork in order to share memory pages.

Unreal Engine C++ API Reference > Runtime > Core > Misc

References

   
Module Core
Header /Engine/Source/Runtime/Core/Public/Misc/Fork.h
Include #include "Misc/Fork.h"

Syntax

class FForkProcessHelper

Remarks

Helper functions for processes that fork in order to share memory pages.

About multithreading: When a process gets forked, any existing threads will not exist on the new forked process. To solve this we use forkable threads that are notified when the fork occurs and will automatically convert themselves into real runnable threads. On the master process, these forkable threads will be fake threads that are executed on the main thread and will block the critical path.

Currently the game code is responsible for calling Fork on itself than calling FForkProcessHelper::OnForkingOccured to transform the forkable threads. Ideally the fork point is done right after the game has loaded all the assets it wants to share so it can maximize the shared memory pool. From the fork point any memory page that gets written into by a forked process will be transferred into a unique page for this process.

Functions

  Type Name Description
Public function Static FRunnableThread *

CreateForkableThread ( FRunnable* InRunnable,
const TCHAR* InThreadName,
uint32 InStackSize,
EThreadPriority InThreadPri,
uint64 InThreadAffinityMask,
EThreadCreateFlags InCreateFlags
)

 Creates a thread according to the environment it's in: In environments with SupportsMultithreading: create a real thread that will tick the runnable object itself In environments without multithreading: create a fake thread that is ticked by the main thread.
Public function Static uint16 Returns the unique index of this forked child process.
Public function Static bool Is this a process that was forked
Public function Static bool Are we a forked process that supports multithreading This only becomes true after its safe to be multithread.
Public function Static bool Returns true if the server process was launched with the intention to fork.
Public function Static void

LowLevelPostForkChild ( uint16 ChildIndex
)

 Performs low-level cross-platform actions that should happen immediately AFTER forking in the CHILD process in a well-specified order.
Public function Static void Performs low-level cross-platform actions that should happen immediately AFTER forking in the PARENT process in a well-specified order.
Public function Static void Performs low-level cross-platform actions that should happen immediately BEFORE forking in a well-specified order.
Public function Static void Event triggered when a fork occurred on the child process and its safe to create real threads
Public function Static void

SetIsForkedChildProcess ( uint16 ChildIndex
)

 Sets the forked child process flag and index given to this child process
Public function Static bool Tells if we allow multithreading on forked processes.

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